Il4-GFP expression does not always correlate with IL-4 protein secretion.7 To determine whether ILC2s were secreting IL-4 in vivo, we infected IL4-GFP/KN2 mice, which express human CD2 on the surface of cells that have translated and secreted IL-4, and analyzed KN2 expression following infection. The gene discussed is IL4; the disease is infection.